You can message other users on ChangeX if they are in the same group as you by clicking on 'message members' or the little speech bubble next to your name.
You can then add the names of the people you wish to message. You will see a list of suggestions based on the groups you are a member of.
As a group admin, you can start a conversation with everyone without having to manually add each member. Navigate to your group page and you will see the "Message Members" and "Message Team" links.
Once you hit send, everyone in your group will be notified. Group messages are ideal for important or private conversations for your group.